Disk arrays are arrangements of disks that are often configured to enhance reliability and/or performance. Because hard disk operation involves mechanical and electronic components and continuous energy consumption, hard disks have many failure modes, which include mechanical failures, electronic failures, and power failures. To improve a reliability and performance of hard disk storage, arrays of hard disks are formed into systems that may employ disk and data redundancy, data partitioning, disk health monitoring, and parity generation and checking techniques. Data are often stored in patterns on the disks in an array to enhance the speed and reliability with which the data may be accessed.
Redundant Array of Independent Disks (RAID) is a storage technology that combines multiple disk drive components into a logical unit. Data is distributed across the drives in one of several ways called “RAID levels”, depending on a desired level of availability and performance. RAID disk array configurations are a set of standard configurations that distribute data across multiple disks, using striping, mirroring and/or parity techniques, to provide various degrees of reliability and/or performance enhancement. Data striping techniques segment logically sequential data, e.g., a file, such that accesses to sequential segments of the data are made to different physical disks. Disk minoring replicates data across multiple physical disks. Various parity techniques enable the detection and often the reconstruction of erroneous or lost data. RAID 5 is a standard RAID configuration that uses striping and parity techniques to enable the data on any one disk in the configuration to be totally reconstructed from error-free data and parity on remaining disks in the array.